CA1145065A

CA1145065A - Semiconductor device made by epitaxial growth

Info

Publication number: CA1145065A
Application number: CA000341796A
Authority: CA
Inventors: Jan Bloem; Cornelis H.J. Van Den Brekel
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1978-12-21
Filing date: 1979-12-13
Publication date: 1983-04-19
Also published as: JPS5588321A; NL7812388A; FR2445020B1; GB2038553B; FR2445020A1; DE2950827C2; DE2950827A1; IT1195749B; GB2038553A; US4389273A; IT7928165A0

Abstract

ABSTRACT:
Growth of a layer from the vapour phase is con-trolled at low temperatures by reactions. The result is a homogeneously thick layer. At high temperatures the layer growth is controlled by diffusion in the gaseous phase. The homogeneity of the thickness may then present problems. At low pressure the temperature range over which the growth is determined kinetically is larger but the temperature is then still too low for monocrystalline growth. According to the invention, for homogeneously thick monocrystalline growth there is started from a gas mixture which is in equilibrium with the material to be grown and growth takes place in a temperature gradient in the direction of flow of the gas mixture.

Description

~5~65 26.10.79 1 PHN 9316 "Method of manufacturing a semiconductor device and semiconductor device manufactured by means of the method."

The invention relates to a method of manufac-turing a semiconductor device in which in an elongate reactor monocrystalline material is g`rown epitaxially on disc-shaped monocrystalline substrates from a gas flow in the longitudinal direction of the reactor, during the epitaxial growth in~the reactor a tempe-rature gradient is maintained in the gas flow in the direction of the gas flow between a cross-section up-stream of the gas flow where a first extreme tempera-ture prevails and a cross-section downstream of the gas flow where a second extreme temperature prevails;
during the epitaxial growth the substrates are pre-sent in a temperature range between the extreme tem~
peratures and epitaxial growth tal~es place at different temperatures, and to a semiconductor device manufac-tured by means o~ the method.
Epitaxial treatments are often used in the manufacture of semiconductor devices. In this manu-facture it is an important problem to obtain epitaxial layers of a sufficiently homogeneous thickness.
It has been found that the growth rate of an epitaxial layer deposit~d from the gaseous phase is little dependent on the temperature at high tem-peratures and is stro~gly dependent on the tempera-ture at low temperatures. This means that at hightemperatures diffusion in the gaseous phase is deci-sive of the growth ra-te and at low -temperatures it is surface reactions which are decisive. The temperature nlust always be so high that the surface mobility is sufficient to obtain monocrystalline layers on mono-crystalline substrates.
The above~described relationsh:ip between growth rate and temperature depends on the overall ~,.

2 PHN 9316 pressure At lower overall pressure the diffusion con-stant is larger and hence the diffusion is decisive to a smaller extent of the growth rate and the temperature over which the growth rate is determined by surface reactions is wider.
If the growth rate is determined by surface reactions the homogeneity of the thickness of the depos-ited layer is very good.
Although at lower pressures over a wide tem-perature range the growth rate is determined by surface reactions, the temperatures in said range are not yet high enough to obtain monocrystalline epitaxial layers of a good quality and with a reasonable growth rate.
Therefore, normally, only polycrystalline layers can be obtained in the said temperature range with a sufficient homogeneity of the layer thickness.
If, in order to obtain monocrystalline layers, higher temperatures are used, the growth rate is deter-mined by diffusion in the gaseous phase and the homo-geneity of the thickness of the deposited layer is often insufficient.
This inhomogeneity is not removed in a method of the kind mentioned in the opening paragraph in which the substrates on which growth has to be effected are placed in a temperature gradient which is adjusted so that, viewed in the direction of the gas flow, the reaction rate increases so as to level-out the influence of the depletion in the gas flow of material to be grown on the growth rate. Moreover, this influence is sub-stantially absent at higher temperatures at ~hich the growth rate is determined by diffusion.
One of the objects of the invention is to pro-vide a method with which thick monocrystalline layers can be deposited homogeneously just at higher temper~
atures in the growth range determined by diffusion.

~5~65 26 r 10 ~ 79 3 PHN 931 6 The invention is based inter alia on the recog-nition that, in addition to variables such as tempera-ture and pressure, concentrations of reaction components in the gaseous phase can also influence the homogeneity of the thickness of the deposited layer to a consider-able extent, and that the end in view is reached in particular when the said concentrations during the growth are near the equilibrium concentrations.
Therefore, the method described in the open-ing paragraph is characterized according to the inven-tion in that there is started from a gas flow contain-ing the reaction components of the growth process in a ` composition which is in equilibrium with the material to be grown at the first extreme temperature prevail-ing upstream of the gas flow and upon traversing thegradient the gas flow is supersaturated with respect to the material to be grown.
The chemical reactions which cause the epi-` taxial growth are often associated with etching reac-tions which produce the opposite effect. Equilibriumoccurs when the growth and etching reactions occur equally rapidly. Since the composition of the gas flow in the temperature gradient will start deviating from the equilibrium composition, a low net growth rate is created.
It could therefore be expected that the rate of the deposition process at higher temperature is again determined by chemical reactions. This is not the case, the rate controlling factor remaining dif-fusion in the gaseous phase. What is true is that thehomogelleity during the deposition increases~-which, as described above, would occur just in processes the rate of which is determined by cherrlical reactions.
This discrepancy can possibly be explained by the fact that the lower net growth rate is the resultant of comparatively large growth and etching rates, in which on the one hand the large growth rate in itself, in a process determined by diffusion, would .. . ..

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26.io.79 ~ PHN 9316 give rise to inhomogeneous growth, namely more rapid deposition in certain placed than in other places, but in which on the other hand the large etching rate in places of rapid growth also means more rapid etching than in the other places so that ultimately homo-geneous growth occurs at a low net deposition rate.
~ hen gas flows are used having compositions which are near the equilibrium, -the g~aseous phase is r~pidly exhausted; but by using a temperature gradient in the direction of flow of the gaseous phase, the quantity of` the reaction component present in the gaseous phase can be used efficiently in that the equilibrium composition of the gas mixture will vary continuously, namely is disequilibrated continuous and equilibrated by deposition formation.
A process determined by diffusion is even necessary in this case because chemical reactions oc-cur rapidly and this is again necessary to have a con-tinuous equilibrium along the temperature gradient.
~hen epitaxy is applied to large substrates, for example, having a diameter from 5 to 10 cm, the temperature gradients to be used need not b~s any ob-jection with a view to, for example, the occurrence of dislocations since the temperature gradients are not directed radially and can be adjusted slowly over the substrates.
It is to be noted that homogeneoùsly thick layers can also be obtained with known methods. In or-der to obtain this, high gas flow rates have to be used~ which involves a high consumption of raw materials, for example a carrier gas. One of the advantagesof the method according to the invention is that no high flow rates need to be used. In fact, high flow rates are not - desired either to obtain equilibrium between glas flow and substratesl Other advantages will become apparent hereinafter.
The method according to the invention has the advantage that also in the range o~ comparatively .

.. . . .... . . . .. . . , . . . ., .. . , j ~5~6~

26.10.79 5 PHN g316 high temperatures and pressure (for example 1 atm.), for which it holds traditionally that the homogeneity is a problem there, homogeneous growth is possible. At high temperatures the surface mobility is sufficient for a good monocrystalline growth and a good homo-geneity may nevertheless occur, as well as at high pressures, in spite of the fact that the rate of the processes is determined by diffus~ion phenomena.
Also as a result of this it is possible to adjust the temperature gradient necessary in the method according to the invention in a compara;tively large temperature range.
The use of a low growth rate does not seem to be attractive for the economy of the epitaxial process.
This apparent disadvantage is compensate~
for by the resulting homogeneity of the deposited layer and by another important advantage. This occurs in a preferred embodiment of the method of the inven-tion in which the disc-shaped substrates are placed with their major surfaces in parallel and at short mutual distances as compared with the dimensions of the major surfaces.
The resulting advantageous high packing den-sity of substrates during the epitaxial depositiondoes not do away with the homogeneity of the thick-ness of the deposited layer. The high packing density of the substrates enables an extremely economical operation inspite of the comparatively low growth rate, since làrge numbers of substrates per batch can be treated.
It is often usual in epitaxy to heat the substrates via a body on which the substrates bear during the epitaxial treatment. The temperature of the substrates is higher than that of the reactor wall so that in general little deposition occurs on the reactor wall (cold-wall reactor).
In a parallel arrangement of the substrates ~. . .. . .. . ... ~ ..

~4S~65 26.10.79 6 PHN 9316 as described above, heating via adjoining bodies is objectionable and this i5 preferably done in a cheap and well-controllable manner via the wall of the reactor (hot-wall reactor). In the last-mentioned preferred em-bodiment, however, a deposition which were to be expect-ed on the reactor wall does not occur since the reaction rate for the deposition is low and the nucleation on the substrate is much stronger than on the reactor wall.
Graphite susceptors are hence not necessary in the last-mentioned preferred embodiment of the method of the invention so that a smaller possibility of con-tamination occurs during the epitaxial growth.
The substrates are preferably accommodated parallel to the direction of the gas flow. In this case the gas flow has the same direction everywhere as the temperature gradient and the growth takes p~ace particularly efficaciously.
Satisfactorily results can be obtained by arrailging the substrates at an angle between 0 and 90 with the direction of the gas flow; but an ar-rangement of the substrates perpendicular to the di-rection of the gas flow resuits in a less ef~icient growth.
In order to obtain epitaxial growth on one major surfàce of the substrates, the substrates, prior to the epitaxial growtll, are arranged pairwise with their major surfaces against each other, or a major surface of the substrates not to be covered is covered, prior to the epitaxial growth~ with a layer mas~ing against growth.
In order to prevent auto-doping, a substxate is placed with its major surface to be covered opposite to the masking layer of the adjacent substrate.
The substrates may be arranged both horizon-tally and vertically.
In preferred forms of the method of the in-velltion an epitaxial si1icon layer is grown on a silicon ~ 5 26.10.79 7 PHN 9316 substrate from a gas flow containing silicon, ~alogen and hydrogen, chlorine being preferably used as a halogen.
These gas flows are obtained, for example, from silicon compounds, such as silane, nomo, di, tri or tetrachlorosilane, and hydrogen chloride in acldition to hydrogen as a vehicle gas.
Prior to the epitaxial growth at the first extreme temperature, the gas flow is preferably equi-librated with the material to be grown and in the caseof growth of silicon the gas f~ow which is equilibrated contains halogen and hydrogen and is free from silicon.
This synthesis of the gas flow is used in particular together with a negative temperature gra-dient in the epitaxial growth, since it is avoidedthat during the heating of the gas flow deposition of silicon already occurs.
In the method of the invention smaller quan-tities of the conventional vehicle gas hydrogen-are necessary because lower flow rates can be used than in knOWIl methods.
It is known that in the equilibrium system silicon-chlorine-hydrogen the sum of the p~rtial vapour pressure of the silicon compounds depends on the tem-perature and shows a minimum which is more pronouncedaccording as the ratio of the quantity of chlorine present to the quantity of hydrogen present is lar-ger.
When the pressure is increased, the minimum rnoves to higher temperatures, when the pressure is re-duced, or hydrogen is replaced by an inert gas, for example nitrogen, the minimum moves to lower tempera-tures, I
From this it follows that the ternpera-ture gradient may be chosen to be both positive and nega-tive. A positive temperature gradient is used at com-paratively low temperatures and a negative temperature gradient is used at comparatively high temperaturesO

.

~5~6S

26.10.79 8 PHN 9316 An etching process is usually carried out before the epitaxial growth. In the method according to the invention this occurs for reasons analogous to those e~plained above for the growth process in such manner that a homogeneously thick layer is removed if, prior to the epitaxial growth, the substrates are etched in an elongate reactor from a second gas flow in the longitudinal direction of the reactor, in ' which a temperature gradient in the direction of the second gas flow is maintained in the last-mentioned reactor during etching in the second gas flow be-tween a cross-section upstream of the gas flow where a third extreme temperature prevails and a cross-sec-tion downstream of the second gas flow where a fourth extreme tempera-ture prevails, the substrates during etching are situated in a temperature ra~ge'between the last-mentioned extreme temperatures and etching is carried out at different temperatures and there is started from a second gas flow-co~taining the reaction components of the etching process in a composition - ~hich is in equilibrium with the material,to be etched at the third extreme temperature prevailing upstream of the second gas flow and, when the last-mentioned `gradient is traversed~ the second gas flow is under-25 ~ saturated with respect to the material to be etched.
~ tching can be carried out in a simple man-ner if this is carried out in the same reactor in which the epitaxial growth takes place, ' ~tching can even be further simplified if in a homoepitaxial growth process the location of the sub-strates in the reacto-r where etching is carried out is the same as that where epitaxial growth is carried out, the temperature gradient for etching and growing are the same, the second extreme -temperature is'equal to the third and the first ex-treme temperature is equal to the fourth, and the first and second gas flows have opposite directions.
The conditions required for the method ac-~ 5~6 ~ -26.10.79 9 PHN 9316 cording to the invention are extremely suitable for a modified embodiment in which prior to the epitaxial growth the substrates are subjected to an isothermal treatment in a gas flow which is in equilibrium with the material to be treated at the treatment tempera-ture.
In this manner crystal i.mperfections oan be `removed before the epitaxial growth. ~
Thi.s modified embodiment is preferably car-10 ` ried out if the major surface on which -the epitaxial growth is carried out has been~subjected to an ion implantati~on treatment.
The isothermal treatment may be carried out prior to, after or instead of the etching treatment.
For simplicity, therefore, the treatment temperature is equal to the first or the third extreme temperature.
The invention will now be described in greater detail with reference to a few examples and the accompany:ing drawing.
In the drawing, Figure 1 shows diagrammati-cally the relationship between the partial vapour pres~
sure in a gas flow of a material to be grown in the form of compounds and the temperature and Figure 2 is a diagrammatic longi.tudinal sec-; tional view of a part of a reactor for carrying out the method of the invention.
In the present method, monocrystalline material is grown epitaxially on disc-shaped monocrystal-line substrates 23 in an elongate reactor 21 (see Figure 2) from a gas flow in the longitudinal direction 2Z of the reactor 21.
During the epitaxial growth a te~lperature gradient is maintained in the gas flow in the direction 22 of the gas flow between a cross~section 2l~ O.f the reactor upstream of the gas flow ~here a first extreme temperature T1 prevails and a cross-section 25 down-stream of the gas. flow where a second extreme tempe-~ 6 S

26.10.79 1~ PHN 9316 rature T2 prevails.
During the epitaxial growth the substrates23 are in a temperature range between the extreme tem-peratures T1 and T2 and the epitaxial growth takes place~
at different temperatures.
According to the invention there is started from a gas flow containing the reaction components of the growth process in a composition which is in equi-librium with the material to be grown at the first ex-I0 treme temperature T1 prevailing upstream of the gasflow.
For that purpose, the gas flow may be equi-librated with the material 26 to be grown prior to the epitaxial growth at the first extreme temperature T1.
The temperature gradient is adju~ted by heat-ing via the wall of the reactor by means of the heating coil 27.
During traversing the gradient the gas flow is supersaturated with respect to the material to be grown.
This will be explained further with reference to Figure 1.
This Figure shows diagrammatically the sum of the partial vapour pressuresof silicon compounds as a function of the temperature which is obtai.ned when solid silicon is in equilibrium with a gaseous phase havillg a given constant ratio chlorine: hydro-gen and a gi~en constan-t sum of the partial pressures o~ the reactants.
Above the equilibrium curve 11 shown in Fi-gure 1 the gaseous phase is supersa-turated with sili-con and deposition of solid silicon from the gaseous phase may occur; be].ow the equilibrium curve 11 the gaseous phase is undersaturated and etching of sili~
con occurs.
When there is started from a gas flow which has been`equilibrated with silicon at a first extreme temperature T1, the gaseous phase, when the tempera-~58~5 26.10.79 11 P~ 9316 ture is increased, upon traversing the tempera-ture gradient will become supersaturated and deposit silicon from the gaseous phase.
The partial silicon pressure will decrease `5 - to the second extreme temperature T2 in the direction of the temperature gradient. The temperature gradient for epitaxial growth can extend maximally up to the ten~perature Tmin where the partial silicon pressure is minimum.
lOThe temperature gradient in the direction of the gas flow is positive~ The temperature gradient may also be chosen at a higher temperature level. In that case, for example, T4 is the first extreme tem-perature and T is'the second. The same phenomena of

3 occ~
supersaturation and growth ~5~r ~n this case the temperature gradient is negative.
Etching of a substrate can be carried out in a manner analogous to the epitaxial growth, namely also in a gas flow in the longitudinal,direction of an elongate reactor while using a temperature gradient in the direction of the gas flow.
During e-tching, temperature gradients are used which are opposite to those of the epitaxial growth. FOI' example, upon etching, -the ternperature gradient will be maintained be-tween a cross-section of the reactor upstream of the gas flow where a third extreme temperature T3 prevails and a cross-sec-tion do~nstream of the gas f:low where a fourth extreme tem-perature T4 prevails. During etching, the substrates 23 are in a temperature range between extreme tempera-tures T3 and T4 and etching is carried out at dlffererl-t temperatures.
-There is started from a ga,s flow containing : the reaction components of the etching process in a composition which i9 in e~uilibrium with the material - to be etched at the third extreme temperature T3 pre-vailing upstream of the gas flow.' ~ Tpon traversing the gradient, the gas flow s 26.10.79 12 PHN 9316 becomes undersaturated with respect to the material to be etched.
. If silicon is to be etched in the ratio chlorine-hydrogen for which the equilibrium curve shown in ~igure 1 applies, the gaseous phase, upon increasing the temperature from T3 upon traversing the temperature gradient, will become undersa-turated and etching of silicon occurs.
In the direction of the temperature gradient the partial silicon pressure will increase to the fourth extreme temperature T4.`
It will be obvious that upon etGhing, T2 in .~igure 1 may also be chosen for the third extreme tem-perature and T1 in ~igure I may be chosen for the fourth extreme temperature.
For growing and etching the same reactor.is preferably chosen and in homoepitaxy the same tempera-ture gradients and extreme temperatures are .used, the difference between growing and etching consisting of the difference in direction .of the ga.s flow with.res-pect to the temperature gradient.
Preceding the epitaxial growth, the substrates 23 may also be subjected to an isothermal treatment.
This is done in a gas flow which is in equilibrium with the material to be treated at the treating tem-perature.
This may be done, for example, by placing the substrates 23 between the store 26 and the cross-section 2ll and to maintain the first extreme tempera-ture T1 at that area while leading over the gas flowin the direction 22, Of course, the isothermal treatment may.also be carried out prior to an etching t:reatment? for . e~ample, by placing the substrates on the right-halld side of cross-section 25 and passing an equilibrium gas flow over the substra-tes 23 in tlle direction op-posite to the direction 22 at a thermal treatment temperature equal to the third extreme temperature .

5~ ~ ~

26.10.79 13 P~ 9316 The said thermal treatments may be carried out, for example~ when prior to the epitaxial growth the growth surface has been subjected to an ion im-plantation treatment. ~ surface treated by ion implan-tation has local damages having a larger energy contentwhich are dlssolved in a suitable transporting medium, for example the equilibrium gas flow, and are deposited therefrom again in adjacent undamaged places of lower energy content.
~igure 2 shows a suitable arrangement of the substrates 23. They are preferàbly arranged with their major surface in parallel and, compared with the dimen-sions of the rnaj~r surfaces, at short mutual distances and parallel to the gas flow.
Example I
A resistance furnace having three heating zones is used~
The furnace comprises a quartz tube 21 hav-ing an inside diameter of 7 cm. The quartz tube is 3 metres long and projects from the furnace about 70 cm on the side where the first extreme temperature is ad-- justed.
By means of the furnace and corresponding to the first heating zone of the furnace, a first extreme temperature of 960 C is adjusted in the tube over a length of approximately 60 cm.
Over d distance of 60 cm and corresponding to the second heating zone of the surface, a substan-tially linear temperature gradient which is positive in the direction of the gas flow for epitaxial growth is then adjusted terminating in a second extrerne tem-perature of I o40c .
Corresponding to the third heating zone ofthe furnace, a constant temperature of 1040 C is main-tained in the tube over a length of approximately40 cm.
Thirty (110)-oriented disc-shaped substrates of silicon, diameter 5 CID~ thickness 250/urn, are treated .

5~65 26.10.79 14 P~ 9316 simultaneously in one batch. The said substrates are situated horizontally in a rack on a quartz substratum.
The rack is ~0 cm long and comprises 10 substrates at a short mutual distance behind each other and 3 sub-5~ strates one above the other in shelves of the rack ata mutual distance of 1.5 to 2 cm.
The r,ack comprising the substrates is first placed in the part of the tube which is outside the ' furnace, after which there is rinsed with argon or .10 hydrogen,until the whole tube is oxygen-free. All , treatments in gas flows take p`lace at atmospheric pressure. The.rack is then slowly moved into the tube until the whole rack is situated in the part of the tube in which the temperature gradi~nt has been adjusted, Etching may now be carried out.in a usual manner by passing a gas flow containing 0.2 % by vol~lme of hydrogen chloride in hydrogen as a. vehicle gas along the silicon substrates in the initial direc-tion of movcment.
According to the invention, however, etching is carried out in a direction opposite to the initialdirection of movement in a gas flow conslsting of a mixture of 4 parts by volume of dichlorosilane, 10 parts by volume of hydrogen chloride and 86 parts by volume of hydrogen. This gas flow is in equi'l'ibrium with silicon at a temperature of 1040~. The.ratio chlorine to hydrogen i.n this gas flow is approximately 1 : 10. The rate of the gas flow is 10 litres per minute 30 and the duration of etching is from 1 to 10 minutes, During etching the thickness of the substrate decreases by 0.1 to 1/um. Etch-ing is discontinued by rinslng the tube witll h.ydrogen.
- Epitaxial g:ro~-th ta]~es place from a gas flow in the initial direction of movement, the gas flow consisting of a mixtu:re of L~ parts by volume of diChlOrOsila.lle 9 9.2 parts by volume of hydrogen chlo-ride and 86.8 parts by volume of' hydrogen. Th:is gas .. . . . . . . .. .. ...

~5~165 26.10.7g 15 PHN 9316 flow is in equili.brium with silicon at a temperature of 960C. The ratio chlorine to hydrogen in this gas flow is also approximately 1 : 10. The rate of the gas flow is 15 litres pe.r minute and the growth time is, 15 minutes, in which an epitaxial layer is grown in a thickness of approximately 3/um.
Growing is discontinued by rinsing with hydrogen. The rack is then slowly ret'racted and fur-ther cooled in the part of the tube outside the fur-nace. '"
Prior to the growth process the substratesmay be subjected to a thermal treatment in the part of the tube which corresponds to the first heating zone and is kept at 960C. A gas flow is led over hav-ing a composition which is also used in the epitaxialgrowth.
,The etching treatment described may be re-placed entirely or partly by said thermal treatment.
The flow rate of 15 litres per minute used in the epitaxial growth is small compared with a flow rate of approximately 100 litres per minute required is known growth processes and with an arrangement of 10 substrates after each other on one shelf, ~xpensive high-frequency apparatus need not be used for the heating and contamination-causing graphite susceptors are not necessary either. The homogeneity of the thickness of the grown layers is better than that in known growth processes, namely approximately 3%, The same homogeneity applies to the etching.
~!~ , ' . .
This example describes epitaxial growth at higher temperatures while us:ing the same'appara-tus.as in the precèding example.
The first extreme temperature now is 1200 C
and the second ext-reme temperature i.s 1150 C, between which temperatures a -temperature gradient is ad3usted which is negati.~e in the di.rection of t'he gas flow for ' ' ~' 26.10.79 16 Pl-~ 9316 epitaxial growth.
In this example also 30 substrates are used which are arranged in a rack in the same manner as in the preceding example.
The substrates are etched in a usual manner f`or 5 minutes in hydrogen with 0. 2% by volume of hy drogen chloride. For obtaining the gas flow for the epitaxial growth, there is started from a gas mixture having approximately 62 parts by volume of hydrogen, 14 parts by volume of dichlorosilane and 2L~ parts by volume of hydrogen chlor:ide. The ratio chlorine to hydrogen in this gas mixture is approximately 1 : 3.~.
The said composition is substantially the equilibrium composition corresponding to the minimum in the curve o~ Figure 1.
A large number of silicon discs is provided in front of the rack in the part of the tube where the constant temperature of 1200 C prevails. For example, some twenty discs are arranged vertically at a distance from 2 to 5 mm with their large surfaces parallel to the gas flow.
A gas flow of 19.8 litres per minute of the above-described composition from which pi~ior to the contact with the 20 silicon discs no deposition can occur, is equilibrated with said discs at 1200 C after which epitaxial growth on the 30 substrates takes place in the temperature gradient.
The epitax;al growth occurs at a rate of 0.13/um per minu-te. A layer of approximately ~/um is grown in hal~ an hour. The remaining results are ana-logous to those of the preceding example.
It will be obvious that the ;n~ent:ion is not restricted to the examples described. For example, the substrates may be s-tacked advantageously in a furnace tube having a rectangular cross-section, ~or exan1ple~ with two discs beside each other. The distance between the substrates may be chosen to be both smaller alld largcr tllan in the examples.

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~5~65 26.10.79 17 P~ 9316 The operating pressure chosen may be larger or smaller than 1 atm.
It has been found that the quality of the epitaxial layer can still be improved by using a fur-nace tube which is lined internally with silicon ni-tride or consists entirely of silicon carbide or si-licon.
Instead of bearing on a qua~rtz substratum, - the substrates may alternatively be arranged pairwise with their major surfaces agains-t each other. A layer masking against growth may also be used. Au~o doping effects may be counteracted, for example, by placing substrates with their surfaces on which the growth is to be carried out opposite to the masking layer of an adjacent substrate.
Dopants may be incbrporated simultaneously with the epitaxial growth.
- The method according to the invention relates to the manufacture of semiconductor devices in the wide range where epitaxy is used and comprises`inter alia the manufacture of discrete devices, for example, solar cells, transistors and diodes, and of integrated cir-cuits.
Besides for the epitaxial grow-th o~ silicon, ~5 the method of the invention rnay be used for the epi-taxial growth of III ~ V compounds in which these corn-poullds can be transported from a source to the substrate, for examplè, by means of hydrogen chloride.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of manufacturing a semiconductor device in which in an elongate reactor monocrystalline material is grown epitaxially on disc-shaped monocrystalline sub-strates from a gas flow in the longitudinal direction of the reactor; in the reactor during the epitaxial growth a temperature gradient is maintained in the gas flow in the direction of the gas flow between a cross-section upstream of the gas flow where a first extreme temperature prevails and a cross-section downstream of the gas flow where a second extreme temperature prevails; during the epitaxial growth the substrates are present in a temperature range between the extreme temperatures and epitaxial growth occurs at different temperatures, characterized in that there is started from a gas flow containing the reaction components of the growth process in a composition which is in equilibrium with the material to be grown at the first extreme temperature prevailing upstream of the gas flow and upon traversing the gradient the gas flow is super-saturated with respect to the material to be grown.

2. A method as claimed in Claim 1, characterized in that the disc-shaped substrates are placed with their major surfaces in parallel and at a short mutual distance as compared with the dimensions of the major surfaces.

3. A method as claimed in Claim 1 or 2, character-ized in that the temperature gradient is adjusted by heat-ing via the wall of the reactor.

4. A method as claimed in Claim 1 or 2, character-ized in that the substrates are arranged parallel to the direction of the gas flow.

5. A method as claimed in Claim 1 or 2, character-ized in that, prior to the epitaxial growth, the sub-strates are arranged pairwise with their major surfaces against each other.

6. A method as claimed in Claim 1, characterized in that a major surface of the substrates not to be covered is covered with a layer masking against growth prior to the epitaxial growth.

7. A method as claimed in Claim 6, characterized in that a substrate is placed with its major surface to be covered opposite to the masking layer of the adjacent substrate.

8. A method as claimed in Claim 1, characterized in that an epitaxial silicon layer is grown on a silicon substrate from a gas flow containing silicon, halogen and hydrogen.

9. A method as claimed in Claim 8, characterized in that chlorine is chosen as a halogen.

10. A method as claimed in Claim 1, characterized in that prior to the epitaxial growth the gas flow is equilibrated at the first extreme temperature with the material to be grown.

11. A method as claimed in Claim 8 or 10, charact-erized in that the gas flow under equilibration comprises halogen and hydrogen and is free from silicon.

12. A method as claimed in Claim 1, characterized in that prior to the epitaxial growth the substrates are etched in an elongate reactor from a second gas flow in the longitudinal direction of the reactor, in which a temperature gradient in the direction of the second gas flow is maintained in the last-mentioned reactor during etching in the second gas flow between a cross-section upstream of the gas flow where a third extreme tempera-ture prevails and a cross-section downstream of the second gas flow where a fourth extreme temperature pre-vails, that during etching the substrates are situated in a temperature range between the last-mentioned extreme temperatures and etching occurs at different temperatures, and that there is started from a second gas flow which contains the reaction components of the etching process in a composition which is in equilibrium with the mater-ial to be etched at the third extreme temperature pre-vailing upstream of the second gas flow and, upon travers-ing the last-mentioned gradient, the second gas flow is undersaturated with respect to the material to be etched.

13. A method as claimed in Claim 12, characterized in that etching is carried out in the same reactor as in which the epitaxial growth occurs.

14. A method as claimed in Claim 13, characterized in that in a homoepitaxial growth process the place of the substrates in the reactor where etching occurs is the same as that where the epitaxial growth occurs, the tem-perature gradients for etching and growth are the same, the second extreme temperature is equal to the third extreme temperature and the first extreme temperature is equal to the fourth extreme temperature, and the first and second gas flows have opposite directions.

15. A method as claimed in Claim 1, characterized in that prior to the epitaxial growth the substrates are subjected to an isothermal treatment in a gas flow which is in equilibrium with the material to be etched at the treatment temperature.

16. A method as claimed in Claim 15, characterized in that the major surface on which the epitaxial growth occurs has been subjected to an ion implantation treat-ment.

17. A method as claimed in Claim 15 or 16, charact-erized in that the treatment temperature is equal to the first or the third extreme temperature.